Straddle carriers are known in the art and are used at shipping ports to convey shipping containers and to load shipping containers onto a truck, or unload shipping containers from a truck.
These known straddle carriers have an extremely strong and heavy horizontal chassis on which or in which a shipping container can locate. A pair of inverted U-shaped tower assemblies are fixed to, or are part of the horizontal chassis and straddle the shipping container (hence the name straddle carrier). Ground engaging wheels are fixed to the chassis and an operator's cabin is located underneath the chassis but above the ground and usually between the front and rear wheels.
The existing straddle carriers suffer from a number of disadvantages. Firstly, the straddle carriers carry shipping containers at least 1.5 m above the ground surface. Therefore, together with the tower assembly, the height of the straddle carrier is such that it cannot be easily manoeuvred in and out of storage sheds.
Another disadvantage with existing straddle carriers is that by having the shipping container fairly high above the ground, the centre of gravity of the straddle carrier is also fairly high which requires an extremely strong and heavy chassis.
Yet another problem with existing straddle carriers is that the carriers are not readily adapted to accommodate shipping containers of various lengths. That is, shipping containers are known to have lengths of between 20-50 ft., and it is dangerous for a short length straddle carrier to carry a long shipping container due to the overhang of the container from each end of the straddle carrier.
An attempt has been made to overcome the length disadvantage by making the chassis of the straddle carrier telescopic but this adds to the weight and greatly increases the cost of the straddle carrier.
Another type of known container support device is a Container Load Trailer, or CLT. The CLT comprises two separate wheel bogies which can be attached to the front and rear ends of a container. When attached, the container can be towed by a truck. A first main disadvantage with the CLT system is that the bogies are attached to the front and rear of the containers, and as each bogie is about 3 m long, the two bogies add about 6 m to the length of the container. This makes maneuvering and turning of the container extremely difficult.
The second main disadvantage with the CLT system is that it is extremely difficult to load a container to the back of a truck. Typically, the container is loaded lengthwise on the truck, but as the bogies are attached to the front and the end of the container, the truck must reverse sideways under the container and then by a process of repeated forward and rearward movements, maneuver itself such that the container is approximately lengthwise on the truck. The bogies can then be decoupled, but it is found that often the locking slots on the container do not line up with the locking pins on the truck.
The CLT bogies can also be used for sidelifting a container, which allows a truck to move lengthwise underneath the container, overcoming the above disadvantage, but once the truck has left, the bogies need to be decoupled and re-positioned to the front and the end of the container to allow the container to be towed.
A further disadvantage with existing straddle carriers is that the straddle carriers are too large to be portable. That is, a conventional straddle carrier does not fit inside a shipping container. In poorer countries, aid or other goods are shipped in containers for security purposes. The poorer countries rarely have the required straddle carriers or other lifting devices to allow the containers to be readily transported away from the port.
The CLT is designed to fit inside a shipping container, but requires a great amount of assembly and attachment to the container to make it useful.
Yet another disadvantage of existing carriers is that the attachment means to attach the carrier to the container are located at the ends of the container. This does not allow the towers to pivot with respect to the container and therefore the wheels cannot maintain contact with the ground when travelling over rough or uneven ground. The problem can be seen in the drawings. FIG. 22 shows an impression of what may occur if prior art inventions were subjected to uneven ground.
As can be seen from this drawing of a prior art invention, the wheels cannot maintain contact with the uneven ground given that the attachment pins must maintain attachment with the container. This results in an increased bending moment and a large increase in torsional forces which can result in stress cracking and weakening in the load bearing elements of the prior art device.
The present invention is directed to a simple, efficient straddle carrier which can lift and transport shipping containers of any length and which has a low height profile making it more suitable for manoeuvring in and out of storage sheds.